1. Field of the Invention
The present invention relates to a photosensitive resin composition for optical waveguides, and in particular to a photosensitive resin composition for forming optical waveguides having high shape precision, and excellent transmission characteristics under high temperature and high humidity.
2. Description of the Related Art
As we enter the multimedia age, due to demands to increase the capacity and speed of data processing in optical communication systems and computers, optical waveguides have come to receive attention as light transmission media. A silica optical waveguide, which is a typical example of conventional optical waveguides, is generally manufactured through the following steps (1) to (3).
(1) A lower clad layer comprising a glass film is formed on a silicon substrate using a method such as flame hydrolysis deposition (FHD) or CVD.
(2) A thin film of an inorganic substance having a higher refractive index than the refractive index of the lower clad layer is formed on the lower clad layer, and this thin film is patterned using reactive ion etching (RIE), thus forming a core portion.
(3) Furthermore, an upper clad layer is formed using a method of flame hydrolysis deposition.
However, with such a method of manufacturing a silica optical waveguide, there have been problems such as a special manufacturing apparatus being required, and the manufacture taking a long time.
To solve these problems, there has been proposed a method of manufacturing an optical waveguide in which the core portion or the like is formed by irradiating prescribed parts of a silicone composition containing a photopolymerizable component with a prescribed amount of light so as to cure these parts, and then developing the unexposed parts (see Japanese Patent Application Laid-open No. 2000-180643).
Compared with the conventional silica optical waveguide manufacturing method, this method is advantageous in that an optical waveguide can be manufactured in a shorter time and at lower cost. However, this method has constraints such as it being necessary to use a special silicone oligomer.
On the other hand, there has been proposed a radiation-curable composition for forming optical waveguides containing (A) a vinyl polymer having carboxyl groups, polymerizable groups and other organic groups, (B) a compound having at least two polymerizable reactive groups in the molecule thereof, and (C) a radiation polymerization initiator (see Japanese Patent Application Laid-open No. 2003-195079). By means of this composition, an optical waveguide having high shape precision and excellent transmission characteristics can be manufactured.